HANDLING OF CHARACTER STRINGS

HANDLING OF CHARACTER STRINGS

INTRODUCTION:

A string is an array of characters. Any group of characters defined between double quotation marks is a constant string.

Example:

“Man is obviously made to think.”

For example,

printf(“\“Well Done!\” ”);

will output the string

“Well Done!”

while the statement

printf(“WellDone!”);

will output the string

WellDone!

Character strings often used to build meaningful and readable programs.

The common operations performed on character strings are:

   Reading  and Writing strings

   Combining strings together.

   Copying one  string to another.

   Comparing strings for equality.

   Extracting a portion of a string.

DECLARING AND INITIALIZING STRING VARIABLES:

A string variable is any valid C variable name and is always declared as an array. The general form of declaration of a string variable is

                           char string_name[size];

The size determines the number of characters in the string-name.

Some examples are:

char city[10];

char name[30];

Reading a Line of Text:

In many text processing applications, we need to read in an entire time  of text from the terminal. It is not possible to use scanf function to read a line  containing more than one word. This is because the scanf terminates reading

as soon as a space is encountered in input. We have learned to read a single character from the terminal, using the

function getchar.

WRITING STRINGS TO SCREEN

We have used the printf function with %s format to print strings to the  screen. The format %s can be used to display an array of characters that is terminated by the null character. For example, the statement

                                          printf(“%s”, name);

can be used to display the entire contents of the array name.

The following features of the %s specifications.

1. When the field width is less than the length of the string, the entire string is printed.

2. The integer value on the right side of the decimal point specifies the number of characters to be printed.

3. When the number of characters to be printed is specified as zero, nothing is printed.

4. The minus sign in the specification causes the string to be printed left-justified.

                          printf(“%*.*s\n”, w, d, string);

OPERATIONS ON CHARACTERS

C allows us to manipulate characters the same way we do with numbers. Whenever a character constant or character variable is used in an expression, it is automatically converted into an integer value by the system. The integer value depends on the local character set of the system. To write a character in its integer representation, we may write it as an integer. For example, if the machine uses the ASCII representation, then,

                        x = ‘a’;

printf(“%d\n”, x);

will display the number 97 on the screen.

In ASCII character set, the decimal numbers 65 to 90 represent upper-case alphabets (A-Z) and 97 to 122 represent lower-case alphabets (a-z).

The values from 91 to 96 are excluded using an if statement in the for loop.

The C labrary supports a function that converts a string of digits into their integer values.

The function takes  the form

x = atoi(string);

STRING - HANDLING FUNCTIONS

The C library supports a large number of string-handling functions that

can be used to carry out many of the string manipulations. Following are the

most commonly used string-handling functions.

                   Function                 Action

                    strcat()                  concatenates two strings

                    strcmp()                compares two strings

                    strcpy()                 copies one string over another

                    strlen()                  finds the length of a string.

                    strrev()                       reversing the string.

                    strlwr()                 converts upper case to lower case.

                    strupr()                converts lower case to upper case.

strcat() Function

The strcat function joins two strings together. It takes the following

form:      strcat(string1, string2);

C permits nesting of strcat functions. For example, the statement

                 strcat (strcat (string1, string2), string3);

#include<string.h>

#include<stdio.h>

void main()

{

  char destination[25]="This is ",c[8] = " Turbo ", turbo[5]=" C++";

   clrscr();

   strcat(destination,c);

   strcat(destination,turbo);

   printf("%s\n",destination);

   getch();

}

strcmp() Function

The strcmp function compares two strings identified b the arguments and has a value 0 if they are equal. If they are not, it has the numeric difference between the first non matching characters in the strings. It takes the form:

                         strcmp(string1, string2);

string1 and string2 may be string variables or string constants. Examples are:    

       strcmp(“Rom”, “Ram”);

#include<string.h>

#include<stdio.h>

void main()

 {

    char buf1[10],buf2[10];

    int ptr;

    clrscr();

    printf("enter two strings :");

    scanf("%s %s",buf1,buf2);

    ptr=strcmp(buf2, buf1);

    printf("diff =%d\n",ptr);

    if(ptr==0)

       printf("two strings are equal\n ");

   else if (ptr > 0)

       printf("\nbuffer 2 is greater than buffer 1\n");

    else

       printf("buffer 2 is less than buffer 1\n");

       getch();

  }

                      

strcopy() Function

The strcpy function works almost like a string-assignment operator. It takes the form

                           strcpy(string1, string2);    

For example, the statement

strcpy(city, “DELHI”);     

#include<stdio.h>

#include<string.h>

void main()

 {

    char string[10];

    char str1[10]="abcdefghi";

    clrscr();

    strcpy(string,str1);

    printf("%s\n", string);

    getch();

 }

strlen() Function

This function counts and returns the number of characters in a string.

n = strlen(string);

         where n is an integer variable which receives the value of the length of the string.

#include<stdio.h>

#include<conio.h>

#include<string.h>

void main()

{

   int l=0;

   char string[25]="Borland International";

   clrscr();

   l=strlen(string);

   printf("%d\n",l);

   getch();

}

/* A program is to find the reverse of a string */

#include<stdio.h>

#include<string.h>

#include<conio.h>

void main()

{

   char forward[10] = "string";

   clrscr();

   printf("Before strrev(): %s\n",forward);

   strrev(forward);

   printf("After strrev():  %s\n",forward);

   getch();

}

/* A program is to convert upper case to lower case */

#include <stdio.h>

#include <string.h>

void main()

{

   char string[25] = "BorlandInternational";

   clrscr();

   printf("string prior to strlwr: %s\n", string);

   strlwr(string);

   printf("string after strlwr:    %s\n", string);

   getch();

}

/* A program is to find the  converts lower case to upper case  */

#include <stdio.h>

#include <string.h>

void main()

{

   char string[25] = "BorlandInternational";

   clrscr();

   printf("string prior to strupr: %s\n", string);

   strupr(string);

   printf("string after strupr:    %s\n", string);

   getch();

}